Simulation of Alfvén eigenmodes destabilized by energetic electrons in tokamak plasmas

Todo, Y.; Wang, Hao; Wang, Jialei

doi:10.1088/1741-4326/ab6c79

Cited by 21 publications

(32 citation statements)

References 53 publications

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“…[31] In this cases, the mode frequencies are higher than that in NBI heated plasma and profiles of energetic electrons are proved to play an important role in evolution of TAEs. [32] Reversed shear Alfvén eigenmode (RSAE) is one of typical core localized electromagnetic instabilities in reverse magnetic shear plasma and characterized by frequency sweeping slowly due to slight change of minimum safety factors. [34] As 𝑞 min (𝑡) changes during the discharge, RSAE frequency alters at a rate 𝑑 𝑑𝑡 𝜔 RSAE (𝑡) ≃ ±𝑚 𝑉A 𝑅 𝑑 𝑑𝑡 𝑞 min (𝑡).…”

Section: Reviewmentioning

confidence: 99%

Energetic Particle Physics on the HL-2A Tokamak: A Review

Shi¹,

Chen²,

Duan³

2021

Chinese Phys. Lett.

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Interaction between shear Alfvén wave (SAW) and energetic particles (EPs) is one of major concerns in magnetically confined plasmas since it may lead to excitation of toroidal symmetry breaking collective instabilities, thus enhances loss of EPs and degrades plasma confinement. In the last few years, Alfvénic zoology has been constructed on HL-2A tokamak and series of EPs driven instabilities, such as toroidal Alfvén eigenmodes (TAEs), revered shear Alfvén eigenmodes (RSAEs), beta induced Alfvén eigenmodes (BAEs), Alfvénic ion temperature gradient (AITG) modes and fishbone modes, have been observed and investigated. Those Alfvénic fluctuations show frequency chirping behaviors through nonlinear wave-particle route, and contribute to generation of axisymmetric modes by nonlinear wave-wave resonance in the presence of strong tearing modes. It is proved that the plasma confinement is affected by Alfvénic activities from multiple aspects. The RSAEs resonate with thermal ions, and this results in an energy diffusive transport process while the nonlinear mode coupling between core-localized TAEs and tearing modes trigger avalanche electron heat transport events. Effective measures have been taken to control SAW fluctuations and the fishbone activities are suppressed by electron cyclotron resonance heating. Those experimental results will not only contribute to better understandings of energetic particles physics, but also provide technology bases for active control of Alfvénic modes on International Thermonuclear Experimental Reactor (ITER) and Chinese Fusion Engineering Testing Reactor (CFETR).

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Section: Reviewmentioning

confidence: 99%

Energetic Particle Physics on the HL-2A Tokamak: A Review

Shi¹,

Chen²,

Duan³

2021

Chinese Phys. Lett.

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“…During tokamak discharges, the q min usually decreases due to the diffusion of plasma current toward the magnetic axis [21]. Consequently, the equilibrium evolution of reversed shear plasmas causes the frequency sweeping of RSAEs and the transition between RSAEs and toroidal Alfvén eigenmodes (TAEs) [22][23][24][25][26][27][28]. To be more specific, the RSAE frequency sweeps downwards while the current ramps up for q min > m/n and reaches the minimum frequency when q min = m/n.…”

Section: Introductionmentioning

confidence: 99%

Global kinetic-MHD simulations of downward-sweeping reversed shear Alfvén eigenmodes in tokamak plasmas

Ge¹,

Wang²,

Wang³

2021

Nucl. Fusion

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Hybrid simulations are performed to investigate the dependence of downward sweeping reversed shear Alfvén eigenmodes (RSAEs) on key parameters in tokamaks. The investigation is mainly focused on downsweeping RSAEs with a toroidal number 3 n  . It is found that the occurrence of downward sweeping RSAEs strongly depends on the bulk plasma profiles, including pressure profile and safety factor profile. The influence of bulk plasma pressure value and pressure gradient at min q on downsweeping RSAEs are studied, respectively. It is shown that the excitation of downsweeping RSAE is more associated with the plasma pressure gradient at min q than that with the pressure value. The enhancement of pressure gradient at min q improves the likelihood of the destabilization of downsweeping RSAEs. Moreover, the downsweeping RSAEs only occur in a weak magnetic shear configuration in our simulations. By increasing magnetic shear strength of central plasmas, it is numerically verified that the downsweeping RSAE activities are suppressed and eventually replaced by toroidal Alfvén eigenmodes (TAEs). Following this process, the transition region from TAEs to RSAEs is shifted to a region with lower min q values. In this work, the downsweeping RSAE, which has been confirmed that the mode is in the nonperturbative regime, has a twisted mode structure in the poloidal plane, while the upsweeping RSAE, which is in the perturbative regime, has an up-down symmetry mode structure (no shearing). Further, downward sweeping RSAEs, showing a relatively narrow mode spatial profile, are generally more stable than the upward sweeping ones, which can be a reason why the downsweeping RSAEs are rare in experiments. Finally, it is found that the kinetic effect of energetic ion central pitch angle does not affect the excitation of downward sweeping RSAEs, but affects the mode stability.

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“…DOI: 10.1088/0256-307X/39/10/105201 Interactions between shear Alfvén wave (SAW) and energetic particles (EPs) have become a major concern in plasma physics. [1,2] Because the wave-particle interaction usually gives rise to energetic particle driven instability, such as toroidal Alfvén eigenmode (TAE), [3][4][5][6] reversed shear Alfvén eigenmode (RSAE), [7][8][9][10][11] beta induce Alfvén eigenmode (BAE), [12][13][14] and energetic particle mode (EPM). [15,16] Among those Alfvénic modes, TAEs are most famous due to their spacial mode structure, which may enhance plasma transport.…”

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Observation and Simulation of n = 1 Reversed Shear Alfvén Eigenmode on the HL-2A Tokamak

Shi

Yang

Chen

et al. 2022

Chinese Phys. Lett.

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A branch of high frequency Alfvénic mode is observed on the HL-2A tokamak. The electromagnetic mode can be driven unstable in the plasma with an off-axis neutral beam heating. Its mode frequency keeps almost unchanged or presents a slow-sweeping behavior, depending on the detail current evolution. The poloidal and toroidal mode numbers are $m/n=1/1$. The mode has a quite short duration ($\leq20 $ ms) and usually appears 5-10 ms after the neutral beam being injected into the plasma. Hybrid simulations based on M3D-K have also been carried out. The result suggests that co-passing energetic particles are responsible for the mode excitation. The simulated mode structures are localized nearby location of minimum safety factor ($q_{min}$) and agree with the structures obtained through tomography of soft x-ray arrays. Further, the modes are localized in the continuum gap and their frequencies increase with variation of $q_{min}$ in a wide range. Last but not least, the characteristic of unchanged frequency on experiment is also reproduced by the nonlinear simulation with a fixed safety factor. All those evidences indicate that the $n=1$ high frequency mode may belong to a reversed shear Alfvén eigenmode (RSAE).

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Simulation of Alfvén eigenmodes destabilized by energetic electrons in tokamak plasmas

Cited by 21 publications

References 53 publications

Energetic Particle Physics on the HL-2A Tokamak: A Review

Energetic Particle Physics on the HL-2A Tokamak: A Review

Global kinetic-MHD simulations of downward-sweeping reversed shear Alfvén eigenmodes in tokamak plasmas

Observation and Simulation of n = 1 Reversed Shear Alfvén Eigenmode on the HL-2A Tokamak

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